Classifier with rifflers and variable throat

ABSTRACT

In a classifier for separating particle fractions of different densities from a liquid-borne stream, means are provided to gently open a bed of heavier particles and release lighter particles entrapped adjacent the chamber wall by the heavier particles, thereby permitting the lighter particles to be displaced and move centrally for more complete separation. An adjustable throat between the lower end of the overflow pipe and the underflow outlet is provided by a telescoping external support for the overflow pipe above the cover plate.

United States Patent Loughner 1 June 3, 1975 [54] CLASSIFIE W RIFFLERSAND 3,389,793 3132: lgeleman 583%}: 3,399,770 a omon VARIABLE THROAT3,620,370 11/1971 Swayze 209/144 Inventor: Ja s Loughner, Rt. No. 1, BoxR26,72O 11/1969 Visman 209/211 456, Litton Heights, Scott Depot, 25560Primary Examiner-Frank W. Lutter [22] Filed: Oct. 1, 1973 AssistantExaminer-Ralph J. Hill pp No: 402,193 Attorney, Agent, or Firm-Wood,Herron & Evans 52 us. or 209/211; 209/506 [57] ABSTRACT [51] Int. Cl.B041: 5/103 In a classifier for separating particle fractions of differlField fl 209/2 1. 1 ent densities from a liquid-borne stream, means are210/512 5/ provided to gently open a bed of heavier particles andrelease lighter particles entrapped adjacent the cham- [56] ReferencesCited ber wall by the heavier particles, thereby permitting UNITEDSTATES PATENTS the lighter particles to be displaced and move cen- 624684 5H8 Richards 209/58 trally for more complete separation. Anadjustable 6311:1109 8/1899 Aberg....::III:21:12:: 209/211 throatbetween the lower end Ofthe Overflow P p and 1,149,463 8/1915 Pardee209/211 x the underflow Outlet is Pwvided y a telescoping 1,832,25611/1931 Stebbins................ 209/144 ternal support for the overflowpipe above the cover 2,102,525 12/1937 Freeman 209/211 plate. 2,743,8155/1956 Goodwin 209/211 2,976,994 3/1961 Rodman et al. 209/211 5 Claims,2 Drawing Figures wr f .f/ g I, F

a L .54 J0 4; 35 &J7 J9 s I 1. 4 /'J5 9 x 135 Z 11 2 Q a g 2 5 5 s 2 1 g/M -vfl 55 l 1 l 2/ s i 1 1 li a a 11 LEI CLASSIFIER WITH RIFFLERS ANDVARIABLE THROAT This invention relates to apparatus for separatingheavier or lighter fractions from a liquid-borne stream which carries amixture of particles of different densities. Devices of this generaltype are commonly known as classifiers and are useful, by way ofexample, for separating and recovering coal (lighter) particles from anadmixed rock (heavy) fraction in a water-borne stream.

The invention is particularly directed to classifiers of the centrifugalvortex type, in which the feed stream is directed tangentially into anannular chamber so that as it swirls around the chamber centrifugalforce tends to cause the heavier particles to move along the wall of thechamber while the lighter fraction circulates inwardly of the heavierparticles, closer to the center of the chamber. A lighter fraction istaken off upwardly through an overflow pipe that projects axially intothe chamber, while the heavier fraction is withdrawn downwardly throughan underflow orifice at the bottom of the chamber. To the extent thatthe heavier particles are incompletely or imperfectly separated from thelight, or vice versa, process economics are adversely affected, and itis generally desirable to obtain as clean a separation as possible,consistently with the practicalities involved.

It is my belief that imperfect separation is caused, at least in part,from entrapment" of lighter particles by an overlying circulating layerof heavier particles. More specifically, it is theorized that, ascentrifugal force acts on the mixed density particles as they swirlaround the chamber and causes the heavier fraction to gravitate closerto the wall than the lighter particles, some light particles areoccluded between the heavier particles and the chamber sidewall. Theselighter particles if not thus entrapped would tend to be displacedinwardly toward the axis, but they are hindered from doing so by theheavier particles which overlie them and which tend to hold them againstthe outside wall.

This invention is predicated in part upon the concept of jigging" orgently agitating the particles as they swirl over the wall of thechamber, that is, causing them to move inwardly, then outwardly again,along an undulating path. In accordance with this aspect of theinvention, jigging means are provided to lightly disrupt the otherwisegenerally circular paths of movement of the particles around the chambersidewall, and impart a wavy or sinuous motion which causes the heavierparticles to tumble slightly or at least move relatively apart so thatthe entrapped lighter particles are provided an escape path to move awayfrom the wall and inwardly of the heavier particles. The jigging meansare referred to as rifflers herein, and comprise rounded semicircularprojections, such as half-round bars, which are mounted at spacedpositions within the chamber. These rifflers present gradually inclinedleading and trailing surfaces to the liquid-borne stream as it movesacross them, and gently agitates or jigs the particles adjacent the wallmoving over them, but without creating such great turbulence as to remixthe separated particles and thereby hinder the classification. Theproper jigging action is manifested by release of entrapped particlesand a better separation than would otherwise be obtained.

It is critical to the invention that both the leading and the trailingsurface of the rifflers must not be angular nor present a steep or sharpangle to the stream; that is, both surfaces must be gradually angulated,as opposed to a right-angular or steep face. This avoids the formationof a dead space directly in front of, or be hind, the riffler, and thecreation of turbulence which would counteract the separation otherwisetaking place. Surprisingly, l have found that small half-round bars,having a height not more than about one-third the diameter of thelargest particles being treated, work very effectively for this purpose.

The rifflers are mounted to the cylindrical wall of the chamber, betweenthe inlet and the outlet. They are angulated with respect to thedirection of fluid flow, so that particles move over, rather thanparallel to, the rifflers. Below the cylindrical part of the chamber,the wall leads to a bowl portion wherein the wall curves downwardly andinwardly toward a central opening or cone. It is important that thisbowl curve gradually from a steeply inclined upper region, to an almosthorizontal central region. It is desirable that this bowl have aspherical curvature, with a generally constant radius of curvature, atleast approximately equal to the width of the annular space between theoverflow pipe and the chamber cylindrical wall. This preventsaccumulation or hang-up of solids that might otherwise retard flow tothe overflow outlet.

Another aspect of the invention involves the provision of a variablethroat for a classifier. In accordance with this aspect, means areprovided whereby the throat, i.e., the vertical spacing between thelower end of the overflow tube and the cone at the bottom of thechamber, can readily be adjusted or varied from the outside while theclassifier is in use. In practice, the nature of the *cut" between theheavier and the lighter fractions, i.e., the division between thedensities of lighter particles that come off through the overflow pipeand the density of heavier particles which are taken off downwardlythrough the cone, depends upon the spacing between the two opposedoutlets. The greater the spacing, the lower the mean density of theparticles taken off through the overflow pipe.

In the past, the overflow pipe has commonly been fixed with respect tothe body so that it was difficult to make any adjustment or change inthe throat spacing, at least without disassembling the classifier orremoving the top closure. In accordance with this invention, avertically adjustable overflow pipe is provided so that the throatdimension can be changed as may be desirable for different cuts or fordifferent feed streams.

More specifically, an opening is provided in the body top cover and acircular sleeve is mounted axially to the cover around this opening. Theoverflow pipe telescopes or is slidable axially within this sleeve, inthe upward or downward direction with respect to the outlet. A gasket isprovided around the overflow pipe to seal it while maintainingshiftability of the overflow pipe. The overflow pipe has a diameterwhich substantially corresponds to the diameter of the cone at the pointwhere the latter joins the curved bowl. A flange is mounted to theoverflow pipe above the top cover, through which pass fixed upstandingthreaded rods, and nuts on these rods support the flange and, hence, thepipe. The position of the overflow pipe with respect to the outlet canbe adjusted by shifting the nuts as appropriate to shift the lower endof the pipe upwardly or downwardly within the chamber. Lock nuts securethe pipe in the desired vertical position.

By these throat adjusting means it is readily possible to change the cuteven while the classifier is in use. This enables the device to be setor adjusted as may be desired in response to an analysis of thefractions which are being taken. or to change in input.

Both aspects of the invention can best be further described by referenceto the accompanying drawings in which.

FIG. 1 is a vertical axial section of a preferred form of classifier inaccordance with the invention, and

HG. 2 is a horizontal section taken on line 22 of FIG. 1, and shows thejigging affect of the rifflers on the circulating fluid stream.

The classifier has a main body portion generally at which may be formedof cylindrical pipe. The body 10 has an annular or cylindrical insidesurface 11 which defines an internal chamber 12. An inlet pipe 14 ismounted to body 10 in such manner that it opens generally tangentiallythrough wall 11 to the chamber 12 (see FIG. 2). through an inlet opening15 which is generally adjacent the top of the chamber 12.

At the lower end of the body 10 an annular flange 16 is secured, towhich a flat bottom plate 17 is mounted, as by bolts 18. Bottom plate 17supports an annular casting or bowl 20 which has an inner surface 19that curves from an almost vertical upper region 21 adjacent the insidewall 11 of body 10, downward and inwardly to an almost horizontalsurface region 22 where it joins a central conical opening or cone 23along a circular line 24. The bowl or casting 20 may be formed ofNiehard or other hard metal or ceramic material. Cone 23 leads to anunderflow orifice 25 which is mounted below bottom plate 17. Thisorifice 25 has a generally conical shape and a smaller apex angle thancone 23, and leads to a take-off means or a receiver for the heavierfraction which may be conventional in form.

A top plate or cover 26 is mounted across the top of the body 10 andsecured to a pheripheral flange 27 as by bolts 28. A central opening 30is formed in cover 26 and a cylindrical sleeve 31 is fastened as bywelding around the opening. Preferably sleeve 31 projects into chamber12 below cover 26, but it may extend above the cover. This sleeve 31 isaligned axially with respect to chamber 12, and functions as a slidingmount for an overflow tube or pipe 35. The diameter of the overflow pipesubstantially conforms to the diameter of the conical surface 23 at theline 24 where the latter surface joins the bowl surface 22 as indicatedby dashed lines in FIG. 1. Overflow tube 35 is sized so that it isslidable vertically within the sleeve 31 and a gasket or seal 36 isprovided around the outside surface of the tube 35, above cover 26, toprevent fluid leakage. The gasket 36 is received and held within aV-shaped annular recess 37 that is defined jointly by two superimposedapertured plates 38 and 39 mounted on cover 26 around the opening 30therein.

Screw adjusting means support the pipe 35 above the cover for changingthe vertical position of the pipe. In preferred embodiment, threadedopenings as at 41 are provided through the plates 26, 38 and 39 at anumber of angular positions thereon, and threaded rods or bolts 44 aresecured in these openings 41 and locked therein by nuts 45. The rods 44project upwardly generally parallel to the axis of tube 35, and upwardlypass freely through openings 47 formed in a flange plate 49 secured totube 35. Nuts 50 threaded on the respective rods 44 below flange plate49 support the weight of pipe 35 and position it vertically with respectto the underflow orifice. Nuts 51 on the threaded rods 44 above theflange 49 prevent undesired relative movement of the flange plate 49 andpipe 35 in the vertical direction. it will be apparent that by releasingthe nuts and 51 on each of the respective threaded rods 44, the throatdimension or vertical spacing (designated by X in FIG. 1) between thelower end 55 of overflow pipe 35 and cone 23 can be changed. The weightof pipe 35 is usually sufficient that as the nuts 50 are adjusted downwardly on the respective rods 44, the pipe will slide downward bygravity, toward the cone. In this respect the openings 47 in the plate49 through which the rods pass. and the internal dimension of sleeve 31,should be sufficiently large that the overflow pipe 35 can slide withoutjamming as the nuts are incrementally threaded upwardly or downwardly onthe respective rods. Such adjustability permits varying the throatdimension to change the nature of the cut which is taken. Overhead, aflexible connection (not shown) leads from pipe 35 to means for furtherprocessing of the light fraction. which may be conventional.

Rifflers are provided for gently disturbing the nearly laminar flow ofmaterials over the inside wall 11 of the body 10. The rifflers 60 maycomprise vertically oriented lengths of half-round rod, welded to theinside wall 11 and extending at least part of the distance between theinlet opening 15 and the upper bowl surface 21. With respect to thegeneral direction of incoming fluid indicated by the arrow 59 in FIG. 2,each riffler 60 presents a gradually inclined leading surface 61 andtrailing surface 62. That is to say, neither surface is abruptly orperpendicularly angulated with respect to the direction of flow. This isimportant to avoid turbulence which might remix the particles otherwiseseparated, and to achieve a stabilized separation.

The affect of the rifflers is indicated somewhat schematically near theupper right riffler in FIG. 2. Some light density particles (shown assmall particles) 63 are entrapped against the wall 11 by denserparticles 64 (shown as larger particles), and are thereby prevented frombeing displaced inwardly of the heavier particles toward thecentrifugally separated light particles 65. The rifflers open the bed ofheavy particles, as indicated by arrow 66, separating the heavierparticles from one another or otherwise permitting the entrapped lightparticles to be displaced inwardly, as at 67. As previously indicated,the heavy fraction moves to the underflow orifice, and is not remixedsubstantially with lights as they continue to circulate and move towardthe overflow pipe.

In this latter regard. I have found it desirable that the rifflers bequite small in relation to the size of the largest particles in themixture being processed. The height or radial dimension )1 (see FIG. 1)of the rifflers should not exceed about one-third the diameter of thelargest particles (indicated at 68 in FIG. 2, exaggerated in size) forefficient release of entrapped particles consistent with minimization ofseparation loss by remixing. In one specific embodiment of theinvention, by way of example, the chamber inside diameter was 18 inches,the o.d. of pipe 35 was 8 inches, annular width w was 5 inches, rifflerdimension h was one-fourth inch, or 5% of annular chamber width w. fortreating a mixture of particles 1 inch and smaller in size. The verticaldimension of the rifflers was 5 inches. The axial length of chamber wall11, above bowl 20, was equal to the inside chamber diameter, i.e., l8inches. The diameter of the circular join line at 24 was 9 inches. Thepipe was adjustable vertically 4% inches from a minimal throat dimensionx of 2 /2 inches to a maximum of 7 inches. Bowl surface 19 wasapproximately spherical, having a radius of curvature r equal to thedimension between join line 24 and the cylindrical wall 11, i.e., 5%inches. This classifier was used to separate residual coal from aso-called gob or refuse pile. The input feed contained 35% coal (65%rock) by weight; 30% of the input coal was removed, for an approximate86% separation efficiency, at an input rate of 46 tons per hour.

Having described the invention, what is claimed is:

l. A classifier for separating heavier and lighter fractions in aliquid-borne stream of mixed particles of different densities, saidclassifier comprising,

a hollow cylindrical body having a wall defining an annular internalchamber,

a bowl at a lower end of said chamber, said bowl curving downwardly andinwardly from the wall of said body to a conical central opening,

an inlet pipe leading to a substantially tangential inlet openingthrough said wall into said chamber adjacent an upper end of thechamber,

a top cover for said chamber,

an overflow pipe projecting downwardly through said cover and axiallyinto said chamber toward said conical opening, said overflow pipe havingan open lower end positioned above said conical opening and below saidinlet opening,

and a plurality of rifflers mounted to said wall at angularly spacedpositions around said chamber below said inlet opening and above saidbowl,

each said rifi'ler being a projection on said wall extending into saidchamber and having a generally semicircular cross-sectional shape withgradually inclined leading and trailing surfaces thereon,

each riffler extending angularly with respect to the direction of fluidflow over said wall between said inlet opening and said central opening,

the dimension of said rifflers in the direction across the radius ofsaid chamber being no greater than about one-third the diameter of thelargest particles to be separated, said rifflers in use of saidclassifier jigging liquid-borne material passing over them and therebyreleasing lighter particles entrapped by heavier particles so that suchlighter particles move inwardly with respect to the heavier particleswhile said heavier particles continue to move over said wall.

2. The classifier of claim 1 wherein said rifflers comprise half-roundbars welded to said wall around said chamber.

3. The classification of claim 2 wherein three such bars are mounted atequi-angularly spaced positions around said chamber.

4. The classifier of claim 1 wherein said bowl has a spherical curvatureand has a radius of curvature approximately equal to the radialdimension between said wall and said central conical opening.

5. A classifier for separating heavier and lighter fractions in aliquid-borne stream of mixed particles of different densities, saidclassifier comprising,

a hollow cylindrical body having a wall defining an annular internalchamber,

a bowl at a lower end of said chamber, said bowl curving downwardly andinwardly from the wall of said body to a conical opening,

an inlet pipe leading to a substantially tangential inlet openingthrough said wall into said chamber adjacent an upper end of thechamber,

a top cover for said chamber,

a central opening in said cover,

a sleeve secured to said cover around said central opening,

an overflow pipe slidable within said sleeve and projecting downwardlythrough said central opening and axially into said chamber toward saidconical opening, said overflow pipe having an open lower end positionedabove said conical opening and below said inlet opening,

means providing a slidable seal around said overflow screw adjustingmeans supporting said pipe above said cover for changing the verticalposition of said pipe with respect to said conical opening,

and a plurality of rifflers mounted to said wall at angularly spacedpositions around said chamber below said inlet opening and above saidbowl,

each said riffler being a projection on said wall extending into saidchamber and having a generally semicircular cross-sectional shape withgradually inclined leading and trailing surfaces thereon,

the dimension of said rifflers in the direction across the radius ofsaid chamber being no greater than about one-third the diameter of thelargest particles to be separated, said rifflers in use of saidclassifier jigging liquid-borne material passing over them and therebyreleasing lighter particles entrapped by heavier particles so that suchlighter particles move inwardly with respect to the heavier particleswhile said heavier particles continue to move over said wall.

1. A classifier for separating heavier and lighter fractions in aliquid-borne stream of mixed particles of different densities, saidclassifier comprising, a hollow cylindrical body having a wall definingan annular internal chamber, a bowl at a lower end of said chamber, saidbowl curving downwardly and inwardly from the wall of said body to aconical central opening, an inlet pipe leading to a substantiallytangential inlet opening through said wall into said chamber adjacent anupper end of the chamber, a top cover for said chamber, an overflow pipeprojecting downwardly through said cover and axially into said chambertoward said conical opening, said overflow pipe having an open lower endpositioned above said conical opening and below said inlet opening, anda plurality of rifflers mounted to said wall at angularly spacedpositions around said chamber below said inlet opening and above saidbowl, each said riffler being a projection on said wall extending intosaid chamber and having a generally semicircular cross-sectional shapewith gradually inclined leading and trailing surfaces thereon, eachriffler extending angularly with respect to the direction of fluid flowover said wall between said inlet opening and said central opening, thedimension of said rifflers in the direction across the radius of saidchamber being no greater than about one-third the diameter of thelargest particles to be separated, said rifflers in use of saidclassifier jigging liquid-borne material passing over them and therebyreleasing lighter particles entrapped by heavier particles so that suchlighter particles move inwardly with respect to the heavier particleswhile said heavier particles continue to move over said wall.
 1. Aclassifier for separating heavier and lighter fractions in aliquid-borne stream of mixed particles of different densities, saidclassifier comprising, a hollow cylindrical body having a wall definingan annular internal chamber, a bowl at a lower end of said chamber, saidbowl curving downwardly and inwardly from the wall of said body to aconical central opening, an inlet pipe leading to a substantiallytangential inlet opening through said wall into said chamber adjacent anupper end of the chamber, a top cover for said chamber, an overflow pipeprojecting downwardly through said cover and axially into said chambertoward said conical opening, said overflow pipe having an open lower endpositioned above said conical opening and below said inlet opening, anda plurality of rifflers mounted to said wall at angularly spacedpositions around said chamber below said inlet opening and above saidbowl, each said riffler being a projection on said wall extending intosaid chamber and having a generally semicircular crosssectional shapewith gradually inclined leading and trailing surfaces thereon, eachriffler extending angularly with respect to the direction of fluid flowover said wall between said inlet opening and said central opening, thedimension of said rifflers in the direction across the radius of saidchamber being no greater than about one-third the diameter of thelargest particles to be separated, said rifflers in use of saidclassifier jigging liquid-borne material passing over them and therebyreleasing lighter particles entrapped by heavier particles so that suchlighter particles move inwardly with respect to the heavier particleswhile said heavier particles continue to move over said wall.
 2. Theclassifier of claim 1 wherein said rifflers comprise half-round barswelded to said wall around said chamber.
 3. The classification of claim2 wherein three such bars are mounted at equi-angularly spaced positionsaround said chamber.
 4. The classifier of claim 1 wherein said bowl hasa spherical curvature and has a radius of curvature approximately equalto the radial dimension between said wall and said central conicalopening.